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Update, I've had a chance to use the SN754410 on the Mongoose prototype. Looks like a winner. Works fine, runs warm not hot with the two Tamiya motors and gearbox. So looks like the SN754410 is the new Mongoose H-Bridge.

The motors are powered directly from the batteries, the PIC is powered the same way but with a 1N5817 diode between it and the batteries. Two 470uf 6.3V caps on each side plus 0.1uf near the ICs. The ICD2 is on the same side as the PIC. (You need batteries to run the motors)

It's my understanding 1A total, they can be stacked and I will have as much copper on the PCB under the chip as I can put there.

Click to expand...

The info in the datasheet isn't 100% clear on this. At the top, it lists 1A per driver, which would mean 2A per chip, but it's not clear whether or not this is the peak or continuous rating. It's also not clear what kind of failure to expect when the specs are exceeded (it just says, "Look, don't expect it to run properly if you force the specs," standard component rules).

The greatest load I've ever put on one of these h-bridges was trying to stall by hand a geared car window motor. I used one h-bridge, wiring both full h-bridges in parallel for max current. I couldn't stop the motor! And it only pulled about 1.75A peak before my hand cramped. I tried this over and over again, and the same chip still works fine although it got quite warm (check out the current performance vs. chip heat remark in the datasheet, BTW). So maybe the 1A rating per driver is a continuous rating? That would certainly be consistent with the applications I've seen using the SN754410 on various websites, and with the popular notion/manufacturer's claim that the SN754410 is an improvement over the L293.

Someone ought to do some tests on one to check this out - just put a 1.75A load (something like a 12V 20W halogen bulb) on a single SN754410 chip (wired in parallel) and see what happens over time. I'd do it if I had more time on my hands, which I most certainly do not. It might be in your interest, Bill, if you're looking to limit the investment on mass produced Mongooses (Mongeese?). Is it cost effective to include a fuse given the motor ratings, and the cost of the SN754410 (or two to be completely within spec limits)? I bought some fuses when I bought my first batch of SN754410s, but then I realized that in the off-chance I designed something so poorly that it did blow it'd only be slightly more expensive to replace the SN754410 than to replace the fuse, so why bother? Maybe I got ripped off on my fuses, but like I said I never bothered to use them and have yet to wreck a SN754410.

The more I read the info on the TI website, the more I convince myself that it's 1A per driver, not 1A per chip. Geez, look at the mark-up for this chip with a carrier board! I gotta get me a piece of that action...

Well if its 1.1A per side then the Tamiya gearbox will not be a problem. They DO have thermal shutdown so they will stop functioning if they get too hot. The PTC fuses are self resetting and less than $1. Also since the SN754410 should be soldered to the PCB (No socket) to get the best thermal transfer to the PCB.

Wow $26.99 US.

Thermal epoxy and the heatsink on a SN754410 should keep it cool and look cool too.

Here's the first Mongoose prototype photo. It's mostly a bare chassis at the moment. Better photos to follow. The solderless breadboard is just sitting on the chassis, it will have a mounting plate designed for it.